Glioblastoma multiforme (GBM) are the most heterogeneous and lethal of the malignant adult brain tumors. Even with aggressive combination therapies, the prognosis of GBM remains dismal, with median survival of 15 months after diagnosis.1 
Molecular classification of tumors is essential for developing personalized therapies. Although four distinct molecular subtypes have been identified by gene expression-based molecular classification of TCGA samples (i.e., Proneural (PN), Neural (N), Mesenchymal (M) and Classical (C))3,4,33 the prognostic value of this stratification is weak and these subtypes contribute very little to the survival and prognostic stratification of GBMs.
Gene-level analysis of GBM has provided certain prospective gene signatures for the identification of GBM3,4,28,33-36. For example, an 840-gene signature to predict the GBM subtypes was developed by the TCGA network,3 but it is not yet translated to clinical practice. Despite considerable effort, no clinical diagnostic test for GBM subtyping is currently available.